In the arena of athlete muscle performance, it is desirable to create conditions that permit competition or training at higher levels of resistance for a prolonged period of time. However, acute, intense anaerobic use of skeletal muscle often results in impaired athletic performance, with attendant losses in force and work output, and increased onset of muscle fatigue, soreness, and dysfunction. A single exhaustive exercise session--indeed, any acute trauma to the body such as muscle injury, resistance or exhaustive muscle exercise, or elective surgery--is characterized by perturbed metabolism that affects muscle performance in both acute and long term phases.
Exhaustive exercise depletes metabolic energy carbon sources and acutely disrupts skeletal muscle nitrogen metabolism in three principle ways. (1) Certain amino acids, including branched-chain amino acids, are released from muscle and are deaminated to elevate serum ammonia, oxidized locally as muscle fuel sources, and augment metabolic acidosis. (2) There is a decline in catalytic efficiency of muscle contraction events, as well as an alteration of enzymatic activities of nitrogen and energy metabolism. (3) Protein catabolism is initiated (including decreasing the rate of protein synthesis, as well as increasing degradation of non-contractible protein), thereby reducing long-term strength gains.
Recovery from fatigue during acute and extended exercise is associated with reversal of metabolic and non-metabolic fatiguing factors. Known factors that participate in human muscle fatigue, such as lactate, ammonia, and hydrogen ion, provide an incomplete and unsatisfactory explanation of the fatigue/recovery process, and it is likely that additional unknown agents participate (Baker, A. J., K. G. Koston, R. G. Miller, M. W. Weiner (1993) "Slow force recovery after long-duration exercise: metabolic and activation factors in muscle fatigue" J. Appl. Physiol. 74:2294-2300;Bazzarre, T. L., S. D. Murdoch, S. L. Uw, D. G. Herr, I. P. Snider (1992) "Plasma amino acid responses of trained athletes to two successive exhaustive trials with and without interim carbohydrate feeding" J. Am. Coll. Nutr. 11:505-511; Dohm, G., G. J. Kasperek, E. B. Tapscott, H. A. Barkakat (1985) "Protein metabolism during endurance exercise" Fed. Proc. 44:348-352; Edwards, R. H. T. (1983) "Biochemical basis of fatigue in exercise performance. Catastrophy theory of muscle fatigue" In: Biochemistry of Exercise, Proceedings of the Fifth International Symposium on the Biochemistry of Exercise (H. G. Kutrgen, J. A. Vogel, and J. Poormans, eds.); MacDougall, J. D., M. A. Tarnopolsky, A. Chesley, S. A. Atkinson (1992) "Changes in muscle protein synthesis following heavy resistance exercise in humans: a pilot study" Acta Physiol. Scand. 146:403-404; and Walser, M., N. D. LaFrance, L. Ward, M. A. Van Duyn (1987) "Progression of chronic renal failure in patients given ketoacids following amino acids. Kidney Int. 32:123-128).
.alpha.-ketoisocaproate (.alpha.-KIC) is the ketoacid parent chain of L-leucine (i.e., it is L-leucine without the amino nitrogen), and is the first metabolite in the muscle catabolic pathway of leucine following reversible transamination to glutamate. The intermediary metabolism of .alpha.-KIC and leucine plays a major role in regulatory muscle biochemistry, integrity, and physiology (Abrumrad, N. N., Wise, K. L., Williams, P. E. (1982) "Disposal of .alpha.-ketoisocaproate: roles of liver, gut and kidneys" Am. J. Physiol. 243:E123-E131; Buse, M. G. and S. S. Reid (1975) "Leucine: a possible regulator of protein turnover in muscle" J. Clin. Invest. 56:1250-1261; Flakoll, P. J., M. J. VanderHaar, G. Kuhlman, S. Nissen (1991) "Influence of .alpha.-ketoisocaproate on lamb broth, feed conversion, and carcass composition" J. Anim. Sci. 69:1461-1467; Harper, A. E., R. H. Miller, K. P. Block (1984) "Branched-chain amino acid metabolism" Ann. Rev. Nutr. 4:409-454; Jeevanandam, M., M. R. Ali, N. J. Holaday, J. K. Weis, R. Peterson (1993) "Relative nutritional efficacy of arginine and ornithine salts of .alpha.-ketoisocaproic acid in traumatized rats" Am. J. Clin. Nutr. 57:889-896; and Tarnopolsky, M. A., S. A. Atkinson, J. D. MacDougall, B. B. Senor, P. W. R. Lemon, H. Schwartz (1991) "Whole body leucine metabolism during and after resistance exercises in fed humans" Med. Sci. Sports Exerc. 23:324-333).
In some instances erosion of muscle mass induced by overtraining or injury can be reduced by metabolic intervention (Blomstrand, E. and E. A. Newsholme (1992) "Effect of branched-chain amino acid supplementation of the exercise-induced change in aromatic amino acid concentration in human muscle" Acta Physiol. Scand. 46:293-298; and Mori, E., M. Hasebe, K. Kobayashi, H. Suzuki (1989) "Intermediate stimulation of protein metabolism in burned rats by total parenteral nutrition enriched in branched-chain amino acids" J. Panenter. Enteral. Nutr. 13:(5):484-489) with metabolites of leucine, although in humans leucine itself elevates serum and intramuscular ammonia as it is utilized as a local fuel (MacLean, D. A. and T. E. Grahm (1993) "Branched-chain amino acid supplementation augments plasma ammonia responses during exercise in humans" J. Appl. Physiol. 74:2711-2717 and MacLean, D. A., T. E. Grahm, B. Saltin (1994) "Branched-chain amino acids augment ammonia metabolism while attenuating protein breakdown during exercise" Am. J. Physiol. 267:E1010-E1022). Ammonia (NH.sub.3) arises from the deamination of adenosine monophosphate to inosine monophosphate in the purine nucleotide cycle, as well as from the deamination of branched-chain amino acids. The ability of tissues to re-aminate leucine from supplemental .alpha.-ketoisocaproate has been clinically exploited as a means to treat muscle wasting in acutely traumatized and critically ill patients, while reducing their nitrogen load (Harper, A. E., R. H. Miller, K. P. Block (1984) "Branched-chain amino acid metabolism" Ann. Rev. Nutr. 4:409-454. Traumatized, critically ill hospital patients with eroding muscle mass and nitrogen wasting have been aided with adjuvant dietary intervention using analogs of branched-chain ketoacids and dibasic acids (Mitch, W. E. M. Walser, D. G. Sapir (1981) "Nitrogen sparing induced by leucine compared with that induced by its keto analogue, .alpha.-ketoisocaproate, in fasting obese men" J. Clin. Invest. 67:553-562; Sapir, D. G., M. Walser, E. D. Moyer (1983) "Effects of .alpha.-ketoisocaproate and of leucine on nitrogen metabolism in postoperative patients" Lancet 1:1010-1014; and Warren, B. J., M. H. Stone, J. T. Kearney, S. J. Fleck, R. L. Johnson, G. D. Wilson, W. J. Kraemer (1992) "Performance measures, blood lactate and plasma ammonia as indicators of overwork in elite junior weight lifters" Int. J. Sports Med. 13 :372-376). Hospital and in vitro studies with medical patients exhibiting liver disease and attendant central portal encephalopathy, or renal disease, show that certain administered combinations of ketoacid/amino acid complexes improve muscle trauma recovery time, reduce serum ammonia, enhance injury repair, and yield long-term catabolic/anti-anabolic effects on muscle protein. Acute changes in biceps brachii or quadriceps femoris muscle inter-conversion of KIC and leucine occurs following heavy resistance training (MacDougall et al. (1992) "Changes in muscle protein synthesis following heavy resistance exercise in humans: a pilot study" Acta Physiol. Scand. 146:403-404).
Enhancing muscle recovery following trauma occurs not simply by administering oral or intravenous leucine alone, but instead it responds to increasing the steady-state concentration of .alpha.-ketoisocaproic acid. This anabolic ketoacid is a major factor in reducing protein catabolism, stimulating muscle synthesis, and sparing glucose oxidation, while stimulating insulin release. Indeed, .alpha.-ketoisocaproic acid is superior to leucine in this regard in human and rat muscle studies (Buckspan, R., B. Hoxworth, E. Cersosimo, J. Devlin, E. Horton, N. Abrumrad (1986) "Alpha-ketoisocaproate is superior to leucine in sparing glucose utilization in humans" Am. J. Physiol. 251:E648-E653).
The observed biochemical and physiological effects of oral leucine/.alpha.-KIC on muscle recovery involve several enzymes (Aftring, R. P., K. P. Block, M. G. Buse (1986) "Leucine and isoleucine activate skeletal muscle branched-chain a keto acid dehydrogenase in vivo" Am. J Physiol. 250:E599-E604; Buse, M. G. and S. S. Reid (1975) "Leucine: a possible regulator of protein turnover in muscle" J. Clin. Invest. 56:1250-1261; and Kasperek, G. J. (1989) "Regulation of branched-chain 2-oxo acid dehydrogenase activity during exercise" Am. J. Physiol. 256:E186-E190.): The most critical enzymes are BCAA-aminotransferase, the BCKA dehydrogeneases family, L-leucine dehydrogenase, and 3-methyl-2-oxobutanoate dehydrogenase. Enzyme concentrations of BCAA-aminotransferase are relatively unregulated at fairly steady-state levels in muscle. Therefore, transamination is reversibly catalyzed by BCAA-aminotransferase activity through mass action of available concentrations of .alpha.-ketoisocaproate, L-leucine, L-glutamate, .alpha.-ketoglutarate, and their ancillary metabolites. In the presence of the excessive NH.sub.3 liberated from the purine nucleotide cycle activated during exercise or from glutamate dehydrogenase, L-leucine dehydrogenase provides a beneficial pathway that catalyzes the NH.sub.3 amination of .alpha.-ketoisocaproate to yield L-leucine. The enzyme 3-methyl-2-oxobutanoate dehydrogenase can catalyze the decarboxylation of .alpha.-ketoisocaproate, leading to pathways eventually creating acetoacetate. Alpha-ketoisocaproic acid can be hydrolyzed to beta-hydroxy-betamethylbutyrate via .alpha.-ketoisocaproate dioxygenase. (Harper, A. E., R. H. Miller, K. P. Block (1984) "Branched-chain amino acid metabolism" Ann. Rev. Nutr. 4:409-454; VanKoevering, M., S. Nissen (1992) "Oxidation of leucine and alpha-ketoisocaproate to beta-hydroxy beta-methylbutyrate in vivo" Am. J. Physiol. 262(1 pt 1):E27-31). It has been suggested that beta-hydroxybeta-methybutyrate may be involved in partially preventing muscle degradation and promoting muscle gain in chronic resistance training (Nissen, S. et al. (1996) "Effect of leucine metabolite beta-hydroxy-beta-methylbutyrate on muscle metabolism during resistance-exercise training" J. Appl. Physiol. 81:2095-2104). In contrast to unregulated BCAA-aminotransferase, the activity of BCKA-dehydrogenase is highly regulated during exercise. In muscle and liver, BCKA-dehydrogenase is a multienzyme complex that catalyzes the irreversible oxidative decarboxylation of BCKA, as it reduces NAD to NADH. The activity of BCKA-dehydrogenase greatly increases immediately after strenuous exercise, with subsequent return to resting baseline levels by 10 minutes post-exercise (Kasperek, G. J. (1989) "Regulation of branched-chain 2-oxo acid dehydrogenase activity during exercise" Am. J. Physiol. 256:E186-E190). BCKA-dehydrogenase enzyme activity is regulated by an ATP phosphorylation (inactivation)-dephosphorylation (activation) mechanism. .alpha.-ketoisocaproate is a key stimulator of this enzyme complex, whereby it inhibits the ATP-mediated kinase allosteric inactivation of BCKA-dehydrogenase. The potency of .alpha.-ketoisocaproate is several orders of magnitude greater than any other BCKA BCKA-dehydrogenase activity is therefore mediated by exercise and nutritional factors at the levels of allosteric and substrate mass action.
Control of muscle dysfunction with intravenous or dietary amino acids administered in the purified "free" form, especially branched-chain amino acids (BCAA), has been attempted in many studies (Grunewald, K.K. and R. S. Bailey (1993) "Commercially marketed supplements for bodybuilding athletes" Sports Med. 15:90-103; and MacLean, D. A., T. E. Grahm, B. Saltin (1994) "Branched-chain amino acids augment ammonia metabolism while attenuating protein breakdown during exercise" Am. J Physiol. 267:E1010-E1022). There are no substantiated guidelines for orally supplemented branched-chain amino acids because there have been no reputable double-blind controlled studies conducted to establish their effects; the use of BCAA in athletes is largely anecdotal and without systematic testing of performance. In contrast, however, it has been clearly established that intramuscular protein catabolism is decreased, protein synthesis is increased, and serum ammonia is decreased by metabolic intervention with branched-chain .alpha.-ketoacid (BCKA) analogs of BCAA, and that their effect may be enhanced by simultaneous administration of amino acids (Pui, Y. M. L. and H. Fisher (1979) "Factorial supplementation with arginine and glycine on nitrogen retention and body weight gain in the traumatized rat" J Nutr. 109:240-246; and Smith, K. and M. J. Rennie (1990) "Protein turnover and amino acid metabolism in human skeletal muscle. In: Baillier's Clinical Endocrinology and Metabolism 4:461-498).
L-Arginine is considered a "conditionally essential" amino acid that becomes essential under certain metabolic conditions including muscle trauma and injury (Dundrick, P. S. and W. W. Souba (1991) "Amino acids in surgical nutrition" Surg. Clin. N. Am. 71:459-476 and Smith, K. and M. J. Rennie (1990) "Protein turnover and amino acid metabolism in human skeletal muscle. In: Baillier's Clinical Endocrinology and Metabolism 4:461-498). L-Arginine is a dibasic amino acid that participates in the urea cycle and other intermediary pathways, notably serving as the starting substrate for biosynthesis of polyamines. Polyamines are essential for protein synthesis, and cell growth and proliferation. Arginine synergetically promotes the nitrogen-retaining effects of .alpha.-KIC. Studies show that cationic analogs such as ornithine, citrulline, or lysine may not be as effective as arginine, and may indeed inhibit the cell membrane transporters serving arginine (Kilberg, M. S., B. R. Stevens, D. A. Novak (1993) "Recent advances in mammalian amino acid transport" Annu. Rev. Nutr. 13:137-165; Mitch, W. E., M. Walser, D. G. Sapir (1981) "Nitrogen sparing induced by leucine compared with that induced by its keto analogue, .alpha.-ketoisocaproate, in fasting obese men" J Clin. Invest. 67:553-562; Pan, M., B. R. Stevens, W. W. Souba (1994) "Regulation of intestinal amino acid transport: A surgical perspective" Contemp. Surg. 44:213-220; Pan, M., M. Malandro, B. R. Stevens (1995) "Regulation of System y.sup.+ arginine transport capacity in differentiating human intestinal Caco-2 cells" Am. J. Physiol. 268:G578-G585; and Pan, M. and B. R. Stevens (1995) "Differentiation- and protein kinase C-dependent regulation of alanine transport via system B" J. Biol. Chem. 270:3582-3587).
Previous studies showed that ornithine, lysine, and histidine salts of .alpha.-ketoglutaric acid, beta-hydroxy-beta methylbutyric acid, .alpha.-keto-beta-methylvaleric acid, and other ketoacid analogs of branched-chain amino acids promote positive nitrogen balance (Nissen et al. (1996) "Effect of leucine metabolite beta-hydroxy-beta-methylbutyrate on muscle metabolism during resistance-exercise training" J. Appl. Physiol. 81:2095-2104; VanKoevering, M., S. Nissen (1992) supra; Cynober, L., C. Coudray-Lucas, J -P deBandt et al. (1990) "Action of ornithine .alpha.-ketoglutarate, ornithine hydrochloride, and calcium .alpha.-ketoglutarte on plasma amino acid and hormonal patterns in healthy subjects" J. Am. Col. Nutr. 9:2-12; Cynober, L., M. Vaubourdolle, A. Dore, J. Giboudequ (1984) "Kinetics and metabolic effects of orally administered ornithine .alpha.-ketoglutatarate in healthy subjects fed with a standard regimen" Am. J. Clin. 39:514-519; Funk, M. A., K. R. Lowry, D. H. Baker (1987) "Utilization of the L- and DL-stereoisomers of a .alpha.-keto-.beta.-methylvaleric acid by rats and comparative efficacy of the keto analogs of ranched-chain amino acids provided as ornithine, lysine, and histidine salts" J. Nutr. 117:1550-1555; Sitren, H. S. and H. Fisher (1977) "Nitrogen retention in rats fed on diets enriched with arginine and glycine" Br. J. Nutr. 37:195-208; Visek, W. J. (1986) "Arginine needs, physiological state and unusual diets: A reevaluation" J. Nutr. 116:36-46; and Wolf, J. G. Staleness. In Encyclopedia of Sports Sciences and Medicine, L. A. Larson and D. E. Hermann (Eds) New York: MacMillan Publishing Co. (1971) pgs. 1048-1050). Leucine or other BCAA alone did not demonstrate this effect (Buckspan, R., B. Hoxworth, E. Cersosimo, J. Devlin, E. Horton, N. Abrumrad (1986) "Alpha-ketoisocaproate is superior to leucine in sparing glucose utilization in humans" Am. J. Physiol. 251:E648-E653; Cersosimo, E., B. M. Miller, W. Lacy, N. N. Abrumrad (1983) "Alpha-ketoisocaproate, not leucine, is responsible for nitrogen sparing during progressive fasting in normal male volunteers" Surg. Forum 43:96-98; Sandstedt, S., L. Jorfeldt, J. Larsson (1992) "Randomized, controlled study evaluating effects of branched chain amino acids and .alpha.-ketoisocaproate on protein metabolism after surgery" Br. J. Surg. 79:217-220). Therapeutic strategies for recovery of medical or longitudinal muscle trauma have recently demonstrated the synergistic importance of dibasic amino acid salt complexed with ketoacids. Traumatized, critically ill hospital patients with chronic eroding muscle mass and nitrogen wasting have been aided with adjuvant dietary intervention using analogs of branched-chain ketoacids and dibasic acids (Nitch, W. E., M. Walser, D. G. Sapir (1981) "Nitrogen sparing induced by leucine compared with that induced by its keto analogue, .alpha.-ketoisocaproate, in fasting obese men" J. Clin. Invest. 67:553-562; Sapir, D. G., M. Walser, E. D. Moyer et al. (1983) "Effects of .alpha.-ketoisocaproate and of leucine on nitrogen metabolism in postoperative patients" Lancet 7:1010-1014; Warren, B. J., M. H. Stone, J. T. Kearney, S. J. Fleck, R. L. Johnson, G. D. Wilson, W. J. Kraemer (1992) "Performance measures, blood lactate and plasma ammonia as indicators of overwork in elite junior weight lifters" Int. J Sports Med. 13:372-376).